Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.36   5.154%   $230.6658   $230.67   $230.65   $230.70  
  Purchase #2 $126.90   5.793%   $134.2513   $134.25   $134.25   $134.30  
  Purchase #3 $34.34   6.451%   $36.5553   $36.56   $36.55   $36.60  
  Purchase #4 $18.37   6.656%   $19.5927   $19.59   $19.60   $19.60  
  Purchase #5 $76.25   7.359%   $81.8612   $81.86   $81.85   $81.90  
  Purchase #6 $183.50   12.436%   $206.3201   $206.32   $206.30   $206.30  
  Purchase #7 $246.86   11.850%   $276.1129   $276.11   $276.10   $276.10  
  7 purchase totals = $905.58       $985.3593   $985.36   $985.30   $985.50